1. Field of the Invention
The present invention relates to an electromagnetic actuator including an electromagnet and a permanent magnet, and more specifically relates to such a type of electromagnetic actuator in which a movable member is reciprocatively rotatable.
2. Description of the Related Art
In apparatuses such as cameras which are provided therein with various movable mechanisms, it is often the case that one or more electromagnetic actuators are used as driving sources for the movable mechanisms.
An electromagnetic actuator consisting of an output shaft, a plurality of permanent magnets and a rotary plate stopper has been proposed as a type of electromagnetic actuator in which a movable member is rotated, reciprocatively, in Japanese patent publication No. 2565656 (hereinafter referred to as Patent Document 1), wherein the output shaft is inserted into a hollow portion of a coil and has a rotary plate at one end of the output shaft, the plurality of permanent magnets are arranged at appropriate intervals around the perimeter of the rotary plate, and a rotary plate stopper is installed at a position deviating from the magnetic neutral point of the permanent magnets in a rotational direction of the rotary plate to limit the range of rotation of the rotary plate.
The electromagnetic actuator disclosed in Patent Document 1 is provided with the aforementioned plurality of permanent magnets, which are adopted to give a rotational force to the aforementioned rotary plate mounted to the output shaft of the electromagnetic actuator and the aforementioned rotary plate stopper for limiting the range of rotation of the rotary plate. Therefore, the plurality of permanent magnets and the rotary plate stopper need to be installed around the rotary plate, and also the number of elements of the electromagnetic actuator is large, which becomes an obstacle to miniaturization and weight reduction of the electromagnetic actuator. In addition, since the plurality of permanent magnets need to be arranged and supported so that the N-poles and the S-poles are positioned at 180 degree positions with respect to the rotary plate, and since the rotary plate stopper needs to be provided at a position which deviates from the magnetic neutral point of the permanent magnets in a rotational direction of the rotary plate to hold the rotation position of the output shaft by the rotary plate stopper, the installation positions of the permanent magnets and the shape of the rotary plate stopper need to be designed in an appropriate manner when the range of rotation of the rotary plate, namely, the range of rotation of the output shaft is determined. Consequently, the design for determining the range of rotation of the output shaft becomes complicated, and it becomes difficult to set a desired rotational range for the output shaft. Therefore, to apply the electromagnetic actuator disclosed in Patent Publication 1 to a small apparatus such as a camera, it is desired to achieve a reduction in the number of elements of the electromagnetic actuator and improvements in miniaturization and weight reduction of the electromagnetic actuator.